# RE: Question on H1H2

Title: RE: Question on H1H2

Eric,

a) The answer is your #1 (original ptr +1) for frame N+2.
b) Correct (original ptr +1) for frame N+3, etc.
c) Correct re NDF usage. When NDF is set (inverted), that frame's H1-2 ptr is used.
The following frame has the NDF bits idle, still with the new ptr value.
d) No, the first frame on power up uses the 522 ptr value. When the downstream
ptr processor detects three frames in a row with the same ptr value (522) it will
accept that ptr value as valid.

...Dave

David W. Martin
Nortel Networks
+1 613 765-2901
+1 613 765-0769 (fax)
dwmartin@xxxxxxxxxxxxxxxxxx

=========================

-----Original Message-----
From: Eric Ng [mailto:eng@xxxxxxxxxxx]
Sent: Friday, November 17, 2000 8:39 PM
To: hssg
Subject: Question on H1H2

Hi All,

I have a fundamental problem regarding the operation of
H1 and H2 especially when positive or negative stuffing
occurs.

Example:
in receving frame N
H1[1]H2[1] : 0110_00_10_0000_1010 (default 522)

in receving frame N + 1 (positive stuff opportunity)
H1[1]H2[1] : 0110_00_00_1010_0000

what should i expect in frame N + 2 ?
(1) H1[1]H2[1] : 0110_00_10_0000_1011
(2) H1[1]H2[1] : 1001_00_10_0000_1011 <- inverting NDF
(3) others

would frame N + 3 H1[1]H2[1] be 0110_00_10_0000_1011 ?

For the receive side, the wan phy should be able to
process arbitrary H1H2 pointer.
Should new pointer value only be updated when NDF
is inverted?

Does this mean the very very first frame H1H2 should
actually be H1[1]H2[1] : 1001_00_10_0000_1010 and the
subsequent frames be H1[1]H2[1] : 0110_00_10_0000_1010?

If this is the case, the wan phy could actually miss
the first NDF.  If the default H1H2 is also 522, then
this would not be a problem.  What happen if the frame
pointer value is anything other than 522?  Can the phy
re-sync itself to the correct pointer?

Have a good weekend.

regards,
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